HOW MANY COMMUNITIES ARE TURNING TO TRENCHLESS APPLICATIONS TO SOLVE THEIR MOST DIFFICULT CHALLENGES

“UNDERGROUND, UNDER WHERE?”

Jason T Swartz, P.E. East Region Tunnel Practice Leader

NC AWWA-WEA 96TH ANNUAL CONFERENCE

AGENDA

• Introduction• Technology Overview

• Horizontal Directional Drilling• Microtunneling• Conventional Tunneling

• Case Studies

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INTRODUCTION

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NASTT, North American Society for Trenchless Technology

• Literally “without trenches”

• NASTT utilizes “A family of construction techniques for installing or rehabilitating underground infrastructure with minimal disruption to surface traffic, businesses, and residents”.

• Wikipedia indicates “a type of subsurface construction work that requires few trenches or no continuous trenches”.

DEFINITION OF TRENCHLESS

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Market St Drainage ImprovementsCity of Charleston, SC

• Minimizes social & environmental impacts during construction and operation

• Minimizes existing utility and structure conflicts

• Proven technologies across all ground types and service applications

• Multiple approaches to address the specific needs of the project

WHY TRENCHLESS TECHNOLOGY IS THE SOLUTION

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minimize social impacts minimize environmental impacts

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TRENCHLESS TECHNOLOGY

PIPELINE REPLACEMENT

Conventional Tunneling

Pipe Jacking

Microtunneling

Horizontal Directional Drilling

Pilot Tube / Guided Boring

Auger Boring

Slurry Boring

Water Jetting

Impact Moling

Pipe Bursting

PIPELINE REHABILITAION

LININGS

Sliplining-Cont. Pipes

Sliplining-Short Pipes

Cured in Place Pipe

Deformed Pipe

Spiral Wound Pipe

Segmental Linings

COATINGS

Cast-in-Place Concrete

Reinforced Shotcrete

Spray Applied Linings

PIPELINE REPAIR

Internal Grouting

External Grouting

Mechanical Sealing

Point Repairs

Pointing

• Ground type, conditions, behavior

• Groundwater

• Drive length• Drive depth

• Pipe diameter• Required accuracy

• Application (gravity, pressure)• Location, site availability

• Permitting requirements

• Public Impacts

SELECTION CRITERIA

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• A spiral approach constantly revisiting and challenging assumptions is good engineering practice when managing risk.

RISK MANAGEMENT APPROACH

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POST CONSTRUCTION

CONSTRUCTION

FINAL DESIGN

PREDESIGNALIGNMENT SELECTION

PLANNING

Spiral Analysis

CLASSIC STEPS

Risk register

Risk ranking and probabilities

Mitigation study

Cost evaluation

Risk apportionment

Develop contingencies

Contract and Design Tactics

• Avoiding risk• Select deep vertical alignment to eliminate disturbance to

many urban areas along alignment• Not possible with all risks - can increase cost

• Mitigate risk• Obtain permits and participate in public outreach• Reduces risk to acceptable level

• Allocate risk• Set agreed baselines for geotechnical conditions (risk

sharing)• Disposal of muck (Contractor)• Allocated to party best able to control the risk

MANAGING RISK – THREE STEP PROCESS

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www.ASCE.org

• Risk Register• Geotechnical Baseline Report (GBR)

• Prequalification of Contractors• Design Review Board

• Disputes Review Board

• Clearly defined mitigation measures• Performance vs prescriptive specs

RISK IS MANAGED, NOT IGNORED

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TECHNOLOGY OVERVIEW

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HORIZONTAL DIRECTIONAL DRILLING

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Pilot Tube Installation

Reaming

Pipe Pullback

• Ideal for ground types without rocks and obstructions

• Groundwater is not an issue• Up to four feet in diameter

• Up to a mile in length• Some capacity for vertical and horizontal curves

• A “true” shaft is not needed

• Relatively less accurate (typically not suitable for gravity applications)

• Requires large laydown during pullback operation

• ASTM F1962

HORIZONTAL DIRECTIONAL DRILLING (HDD)

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HDD GROUND APPLICABILITY

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Type of Ground Applicability

Soft to very soft clays, silt, and organic deposits Yes

Medium to very stiff clays and silts Yes

Hard clays and highly weathered shales Yes

Very loose to loose sands (above water table) Yes

Medium to dense sands (below water table) Yes

Medium to dense sands (above water table) Yes

Gravels and cobbles less than 2 to 4in diameter Marginal

Soils with significant cobbles, boulders, and obstructions 4 to 6in diameter

Marginal

Weathered rocks, marls, chalks, and firmly cemented soils Marginal

Significantly weathered to unweathered rock Marginal/No

HORIZONTAL DIRECTIONAL DRILL

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truck-mounted drill rig drill rig

pilot tube breakthroughpilot tube breakthrough

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reamer

reamer

pipe string

pipe string

MICROTUNNELING

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• Form of Pipe Jacking

• ASCE 36-01 Defintion: The tunnel may be considered a microtunnel if all of the following features apply to construction: • the microtunneling boring machine is remote

controlled• a laser guidance system is employed• a jacking system is used for thrust• and continuous pressure is provided to the face of the

excavation to balance groundwater and earth pressures.

• Can be utilized in almost all ground types

• Typically 2 to 10ft diameter, 1,500 ft drive lengths

MICROTUNNELING (MT)

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MICROTUNNEL

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• System Components• MTBM & cutter head• Spoil handling system

(auger or slurry)• Jacking system w/ pipe

sections• Remote control system

• Requirements• Remote controlled• Guided• Jacked pipe• Continuously supported

MICROTUNNEL GROUND APPLICABILITY

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Type of Ground Applicability

Soft to very soft clays, silt, and organic deposits Yes

Medium to very stiff clays and silts Yes

Hard clays and highly weathered shales Yes

Very loose to loose sands (above water table) Yes

Medium to dense sands (below water table) Yes

Medium to dense sands (above water table) Yes

Gravels and cobbles less than 2 to 4in diameter Yes

Soils with significant cobbles, boulders, and obstructions 4 to 6in diameter

Marginal

Weathered rocks, marls, chalks, and firmly cemented soils Yes

Significantly weathered to unweathered rock Yes

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mtbm in jacking pit slurry separation plant

jacking pit pipe about to be pushed

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CONVENTIONAL TUNNELING

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• Manned entry

• Tunnel Boring Machine• Open Face• Closed Face• Slurry• Earth Pressure Balance

• Drill & Blast• “Hand” mined

• Road header• Sequential Excavation Method (SEM) or NATM

“CONVENTIONAL” TUNNELING

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Road Header Hard Rock TBM

Open Face TBM with GrippersOpen Face TBM with Shield

• All ground types• Can handle groundwater

• All drive lengths

• Around 7ft and up

• Highly accurate• All applications• Unique cross sections

• Requires shaft/portal locations• Virtually Unlimited Lengths

“CONVENTIONAL” TUNNELING

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CASE STUDIES

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Prince George’sCounty

Montgomery County

Bi-County Supply Tunnel:• 84-inch finished diameter Pipeline• 5.3 miles length• Depth: 100 to 300 feet• 3-ShaftsBenefits:

• Closes the gap in transmission system

• Improves system reliability

• Increases system capacity

• Helps maintain systempressure

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BACKGROUND – BICOUNTY WATER SUPPLY TUNNEL

Potomac Water Filtration

Plant

WSSC BI-COUNTY WATER SUPPLY TUNNEL

• Main Shaft S3 – Main access for tunneling operations

• 164 ft deep; 35 ft diameter• 5,000 cu yd rock volume

TUNNEL ACCESS SHAFTS

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TUNNEL BORING MACHINE (TBM)

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• TBM – 10-ft diameter x 184-ft. long, 1,200 hp

• Multiple 17-inch diameter carbide disc cutters

• 100 feet per day max rate

“Ms. Colleen”

• Open Cut 27,000 feet of 54-inch dia closed profile wall PVC pipe & 48-inch diameter FRPM pipe.

• Sliplining 5,000 feet of 30 and 36-inch pipe with 24-inch HDPE

• Seven highway and railroad crossing utilizing trenchless methods.

• Trenchless methods included: Microtunneling and Pipe Jacking

GRAND ISLAND, NE WASTEWATER COLLECTION SYSTEM IMPROVEMENTS

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GRAND ISLAND MICROTUNNEL

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GRAND ISLAND PIPE JACKING

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CHARLESTON SEWER TUNNEL PROGRAM

• Phased construction

• 63,200 feet of two-pass tunnels

• 2700 feet of microtunneling

• Fast tracked design and construction

38Charleston, South Carolina

• A history of tunneling in Charleston

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MICROTUNNELING MACHINE

GOOD NEIGHBOR RELATIONS/ FLEXIBLE TEAM APPROACH

• The “Tunneling Advantage” – Public unaware tunnel was being constructed 120 ft below the street…

• Tunnels and trenchless technology have played a very important role in maintaining the City of Charleston’s historic fabric

UNDERGROUND, UNDER WHERE?

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